U.S. patent application number 10/353567 was filed with the patent office on 2003-11-20 for heat resistant aerogel insulation composite, aerogel binder composition, and method for preparing same.
This patent application is currently assigned to Cabot Corporation. Invention is credited to Ackerman, William Clay, Field, Rex James, Poetter, Franz-Josef Heinrich, Scheidemantel, Beate.
Application Number | 20030215640 10/353567 |
Document ID | / |
Family ID | 27669067 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030215640 |
Kind Code |
A1 |
Ackerman, William Clay ; et
al. |
November 20, 2003 |
Heat resistant aerogel insulation composite, aerogel binder
composition, and method for preparing same
Abstract
The invention provides a heat resistant aerogel insulation
composite comprising an insulation base layer comprising
hydrophobic aerogel particles and an aqueous binder, and a
thermally reflective top layer comprising a protective binder and
an infrared reflecting agent. The invention also provides a method
of preparing a heat resistant aerogel insulation composite, as well
as methods of preparing an aerogel binder composition and aerogel
binder compositions so prepared.
Inventors: |
Ackerman, William Clay;
(Cambridge, MA) ; Field, Rex James; (Worms,
DE) ; Poetter, Franz-Josef Heinrich; (Karlstein,
DE) ; Scheidemantel, Beate; (Hanau, DE) |
Correspondence
Address: |
Michelle B. Lando
157 Concord Road
Billerica
MA
01821-7001
US
|
Assignee: |
Cabot Corporation
Billerica
MA
|
Family ID: |
27669067 |
Appl. No.: |
10/353567 |
Filed: |
January 29, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60352671 |
Jan 29, 2002 |
|
|
|
60381215 |
May 15, 2002 |
|
|
|
Current U.S.
Class: |
428/405 ;
428/403 |
Current CPC
Class: |
C09K 21/00 20130101;
B01J 13/0091 20130101; Y10T 428/2991 20150115; Y10T 428/2995
20150115 |
Class at
Publication: |
428/405 ;
428/403 |
International
Class: |
B32B 005/16 |
Claims
What is claimed is:
1. A heat resistant aerogel insulation composite comprising (a) an
insulation base layer comprising hydrophobic aerogel particles and
an aqueous binder, and (b) a thermally reflective top layer
comprising a protective binder and an infrared reflecting
agent.
2. The heat resistant aerogel insulation composite of claim 1,
wherein the hydrophobic aerogel particles have an average particle
diameter (by weight) of about 0. 1-3 mm.
3. The heat resistant aerogel insulation composite of claim 2,
wherein the hydrophobic aerogel particles have an average particle
diameter (by weight) of about 0.5-2 mm.
4. The heat resistant aerogel insulation composite of claim 3,
wherein at least about 95% of the hydrophobic aerogel particles (by
weight) have a particle diameter of about 0.5-2 mm.
5. The heat resistant aerogel insulation composite of claim 1,
wherein the hydrophobic aerogel particles comprise an opacifying
agent.
6. The heat resistant aerogel insulation composite of claim 5,
wherein the opacifying agent is titania, carbon black, or a mixture
thereof.
7. The heat resistant aerogel insulation composite of claim 1,
wherein the hydrophobic aerogel particles comprise fibers.
8. The heat resistant aerogel insulation composite of claim 1,
wherein the hydrophobic aerogel particles are approximately
spherical.
9. The heat resistant aerogel insulation composite of claim 1,
wherein the insulation base layer comprises 5-99 vol. % hydrophobic
aerogel particles.
10. The heat resistant aerogel insulation composite of claim 1,
wherein the insulation base layer comprises a foaming agent.
11. The heat resistant aerogel insulation composite of claim 1,
wherein the insulation base layer comprises 1-95 vol. % of the
aqueous binder.
12. The heat resistant aerogel insulation composite of claim 1,
wherein the aqueous binder is an acrylic binder, a
silicone-containing binder, a phenolic binder, or a mixture
thereof.
13. The heat resistant aerogel insulation composite of claim 12,
wherein the aqueous binder is an acrylic binder.
14. The heat resistant aerogel insulation composite of claim 1,
wherein the aqueous binder is a foamed binder.
15. The heat resistant aerogel insulation composite of claim 1,
wherein the insulation base layer further comprises a flame
retardant.
16. The heat resistant aerogel insulation composite of claim 1,
wherein the insulation base layer is about 1-10 mm thick.
17. The heat resistant aerogel insulation composite of claim 1,
wherein the insulation base layer has a thermal conductivity of
about 40 mW/(m.multidot.K) or less.
18. The heat resistant aerogel insulation composite of claim 1,
wherein the insulation base layer has a density of about 0.5
g/cm.sup.3 or less.
19. The heat resistant aerogel insulation composite of claim 1,
wherein the protective binder is an acrylic binder, a
silicone-containing binder, a phenolic binder, or a mixture
thereof.
20. The heat resistant aerogel insulation composite of claim 19,
wherein the protective binder is an acrylic binder.
21. The heat resistant aerogel insulation composite of claim 1,
wherein the protective binder is a cross-linked binder.
22. The heat resistant aerogel insulation composite of claim 1,
wherein the thermally reflective top layer further comprises an
anti-sedimentation agent.
23. The heat resistant aerogel insulation composite of claim 1,
wherein the infrared reflecting agent comprises metallic
particles.
24. The heat resistant aerogel insulation composite of claim 23,
wherein the metallic particles are aluminum particles.
25. The heat resistant aerogel insulation composite of claim 1,
wherein the thermally reflective top layer further comprises a
flame retardant.
26. The heat resistant aerogel insulation composite of claim 1,
wherein the thermally reflective top layer further comprises
reinforcing fibers.
27. The heat resistant aerogel insulation composite of claim 1,
wherein the thermally reflective top layer further comprises carbon
fibers.
28. The heat resistant aerogel insulation composition of claim 1,
wherein the thermally reflective top layer is about 1 mm thick or
less.
29. A substrate comprising the heat resistant aerogel insulation
composite of claim 1.
30. The substrate of claim 29, wherein the substrate is a component
of a motorized vehicle or device.
31. The substrate of claim 30, wherein the substrate is the
underbody of a motorized vehicle or part thereof.
32. A method for preparing a heat resistant aerogel insulation
composite comprising (a) providing on a substrate an insulation
base layer comprising hydrophobic aerogel particles and an aqueous
binder, and (b) applying to a surface of the insulation base layer
a thermally reflective top layer comprising a protective binder and
an infrared reflecting agent.
33. The method of claim 32, wherein the insulation base layer is
provided by (a) providing a binder composition comprising an
aqueous binder and a foaming agent, (b) agitating the binder
composition to provide a foamed binder composition, (c) combining
the foamed binder composition with the hydrophobic aerogel
particles to provide an aerogel binder composition, and (d)
applying the aerogel binder composition to the substrate to provide
the insulation base layer.
34. The method of claim 32, wherein the insulation base layer is
provided by (a) providing a binder composition comprising an
aqueous binder, (b) providing an aerogel composition comprising
hydrophobic aerogel particles, and (c) simultaneously applying the
binder composition and the aerogel composition to the substrate,
wherein the binder composition is mixed with the aerogel
composition to provide the insulation base layer.
35. The method of claim 32, wherein the insulation base layer is
applied to the substrate by spraying.
36. The method of claim 32, wherein the top layer is applied to the
surface of the insulation base layer by spraying.
37. The method of claim 32, wherein the top layer is applied to the
surface of the insulation base layer while the insulation base
layer is wet.
38. The method of claim 32, wherein the hydrophobic aerogel
particles have an average particle diameter (by weight) of about
0.1-3 mm.
39. The method of claim 38, wherein the hydrophobic aerogel
particles have an average particle diameter (by weight) of about
0.5-2 mm
40. The method of claim 39, wherein at least about 95% of the
hydrophobic aerogel particles (by weight) have a particle diameter
of about 0.5-2 mm.
41. The method of claim 32, wherein the hydrophobic aerogel
particles comprise an opacifying agent.
42. The method of claim 41, wherein the opacifying agent is titania
or carbon black.
43. The method of claim 32, wherein the hydrophobic aerogel
particles comprise fibers.
44. The method of claim 32, wherein the hydrophobic aerogel
particles are approximately spherical.
45. The method of claim 32, wherein the insulation base layer
comprises 5-99 vol. % hydrophobic aerogel particles.
46. The method of claim 32, wherein the insulation base layer
comprises a foaming agent.
47. The method of claim 32, wherein the insulation base layer
comprises 1-95 vol. % of the aqueous binder.
48. The method of claim 32, wherein the aqueous binder is an
acrylic binder, a silicone-containing binder, a phenolic binder, or
a mixture thereof.
49. The method of claim 48, wherein the aqueous binder is an
acrylic binder.
50. The method of claim 32, wherein the aqueous binder is a foamed
binder.
51. The method of claim 32, wherein the insulation base layer
further comprises a flame retardant.
52. The method of claim 32, wherein the insulation base layer is
about 1-15 mm thick.
53. The method of claim 32, wherein the insulation base layer has a
thermal conductivity of about 40 mW/(m.multidot.K) or less.
54. The method of claim 32, wherein the insulation base layer has a
density of about 0.5 g/cm.sup.3 or less.
55. The method of claim 32, wherein the protective binder is an
acrylic binder, a silicone-containing binder, a phenolic binder, or
a mixture thereof.
56. The method of claim 55, wherein the protective binder is an
acrylic binder.
57. The method of claim 32, wherein the protective binder is a
cross-linked binder.
58. The method of claim 32, wherein the thermally reflective top
layer further comprises an anti-sedimentation agent.
59. The method of claim 32, wherein the infrared reflecting agent
comprises metallic particles.
60. The method of claim 59, wherein the metallic particles are
aluminum particles.
61. The method of claim 32, wherein the thermally reflective top
layer further comprises a flame retardant.
62. The method of claim 32, wherein the thermally reflective top
layer is about 1 mm thick or less.
63. The method of claim 32, wherein the thermally reflective top
layer further comprises reinforcing fibers.
64. The method of claim 32, wherein the thermally reflective top
layer further comprises carbon fibers.
65. A method for preparing an aerogel binder composition comprising
(a) providing a binder composition comprising an aqueous binder and
a foaming agent, (b) agitating the binder composition to provide a
foamed binder composition, and (c) combining the foamed binder
composition with hydrophobic aerogel particles to provide an
aerogel binder composition.
66. The method of claim 65, wherein the hydrophobic aerogel
particles have an average particle diameter (by weight) of about
0.1-3 mm.
67. The method of claim 66, wherein the hydrophobic aerogel
particles have an average particle diameter (by weight) of about
0.5-2 mm
68. The method of claim 67, wherein at least about 95% of the
hydrophobic aerogel particles (by weight) have a particle diameter
of about 0.5-2 mm.
69. The method of claim 65, wherein the hydrophobic aerogel
particles are approximately spherical.
70. The method of claim 65, wherein the aerogel binder composition
comprises 5-99 vol. % hydrophobic aerogel particles.
71. The method of claim 65, wherein the aerogel binder composition
comprises 0.1-5 wt. % of the foaming agent.
72. The method of claim 65, wherein the aerogel binder composition
comprises 1-95 vol. % of the aqueous binder.
73. The method of claim 65, wherein the hydrophobic aerogel
particles comprise an opacifying agent.
74. The method of claim 73, wherein the opacifying agent is titania
or carbon black.
75. The method of claim 65, wherein the hydrophobic aerogel
particles comprise fibers.
76. The method of claim 65, wherein the aqueous binder is an
acrylic binder, a silicone binder, a urea-formaldehyde binder, or a
mixture thereof.
77. The method of claim 76, wherein the aqueous binder is an
acrylic binder.
78. The method of claim 65, wherein the aerogel binder composition
has a thermal conductivity of about 40 mW/(m.multidot.K) or
less.
79. The method of claim 65, wherein the aerogel binder composition
has a density of about 0.5 g/cm.sup.3 or less.
80. An aerogel binder composition prepared by the method of claim
65.
81. A method for preparing an aerogel binder composition comprising
(a) providing a binder composition comprising an aqueous binder,
(b) providing an aerogel composition comprising hydrophobic aerogel
particles, and (c) simultaneously applying the binder composition
and the aerogel composition to a substrate, whereupon the binder
composition is mixed with the aerogel composition to provide an
aerogel binder composition.
82. The method of claim 81, wherein the hydrophobic aerogel
particles have an average particle diameter (by weight) of about
0.1-3 mm.
83. The method of claim 82, wherein the hydrophobic aerogel
particles have an average particle diameter (by weight) of about
0.5-2 mm
84. The method of claim 83, wherein at least about 95% of the
hydrophobic aerogel particles (by weight) have a particle diameter
of about 0.5-2 mm.
85. The method of claim 81, wherein the hydrophobic aerogel
particles are approximately spherical.
86. The method of claim 81, wherein the aerogel binder composition
comprises 5-99 vol. % hydrophobic aerogel particles.
87. The method of claim 81, wherein the aerogel binder composition
comprises 0.1-5 wt. % of the foaming agent.
88. The method of claim 81, wherein the aerogel binder composition
comprises 1-95 vol. % of the aqueous binder.
89. The method of claim 81, wherein the hydrophobic aerogel
particles comprise an opacifying agent.
90. The method of claim 89, wherein the opacifying agent is titania
or carbon black.
91. The method of claim 81, wherein the hydrophobic aerogel
particles comprise fibers.
92. The method of claim 81, wherein the aqueous binder is an
acrylic binder, a silicone binder, a urea-formaldehyde binder, or a
mixture thereof.
93. The method of claim 92, wherein the aqueous binder is an
acrylic binder.
94. The method of claim 81, wherein the aerogel binder composition
has a thermal conductivity of about 40 mW/(m.multidot.K) or
less.
95. The method of claim 81, wherein the aerogel binder composition
has a density of about 0.5 g/cm.sup.3 or less.
96. An aerogel binder composition prepared by the method of claim
81.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0001] This patent application claims priority to provisional U.S.
Patent Application No. 60/352,671 filed on Jan. 29, 2002 and
provisional U.S. Patent Application No. 60/381,215 filed on May 15,
2002.
FIELD OF THE INVENTION
[0002] This invention pertains to a heat resistant aerogel
insulation composite, an aerogel binder composition, and methods
for preparing same.
BACKGROUND OF THE INVENTION
[0003] Aerogels are known to provide superior thermal and acoustic
insulation properties. Aerogel insulation materials have been made
by compressing dry particulate aerogel compositions, or by
combining aerogel particles with binders, to provide a cohering
particulate mass. However, dry particle compositions and
aerogel-binder compositions, while providing good thermal and
acoustic insulation, tend to provide little resistance to abrasion
and thermal degradation under high temperature conditions.
[0004] Thus, it would be advantageous to obtain an aerogel
insulation article that provides good thermal and/or acoustic
insulation with improved durability and heat resistance. The
invention provides such an article, as well as a method for
preparing such an article. These and other advantages of the
invention, as well as additional inventive features, will be
apparent from the description of the invention provided herein.
BRIEF SUMMARY OF THE INVENTION
[0005] The invention provides a heat resistant aerogel insulation
composite comprising, consisting essentially of, or consisting of
(a) an insulation base layer comprising, consisting essentially of,
or consisting of hydrophobic aerogel particles, an aqueous binder,
and, optionally, a foaming agent, and (b) a thermally reflective
top layer comprising, consisting essentially of, or consisting of a
protective binder and an infrared reflecting agent. A method for
preparing a heat resistant aerogel insulation composite is also
provided, which method comprises, consists essentially of, or
consists of (a) providing on a substrate an insulation base layer
comprising, consisting essentially of, or consisting of hydrophobic
aerogel particles, an aqueous binder, and, optionally, a foaming
agent, and (b) applying to a surface of the insulation base layer a
thermally reflective top layer comprising, consisting essentially
of, or consisting of a protective binder and an infrared reflecting
agent. In a related aspect, the present invention provides a method
for preparing an aerogel binder composition, which method
comprises, consists essentially of, or consists of (a) providing a
binder composition comprising, consisting essentially of, or
consisting of an aqueous binder and a foaming agent, (b) agitating
the binder composition to provide a foamed binder composition, and
(c) combining the foamed binder composition with hydrophobic
aerogel particles to provide an aerogel binder composition. Also, a
method for preparing an aerogel binder composition is provided,
which method comprises, consists essentially of, or consists of (a)
providing a binder composition comprising, consisting essentially
of, or consisting of an aqueous binder and, optionally, a foaming
agent, (b) providing an aerogel composition comprising, consisting
essentially of, or consisting of hydrophobic aerogel particles, and
(c) simultaneously applying the binder composition and the aerogel
composition to a substrate, whereupon the binder composition is
mixed with the aerogel composition to provide an aerogel binder
composition.
DETAILED DESCRIPTION OF THE INVENTION
[0006] Heat Resistant Aerogel Insulation Composite
[0007] The heat resistant aerogel insulation composite of the
present invention comprises, consists essentially of, or consists
of (a) an insulation base layer comprising, consisting essentially
of, or consisting of hydrophobic aerogel particles, an aqueous
binder, and, optionally, a foaming agent, and (b) a thermally
reflective top layer comprising, consisting essentially of, or
consisting of a protective binder and an infrared reflecting
agent.
[0008] Any suitable hydrophobic aerogel particles can be used in
conjunction with the invention. Suitable hydrophobic aerogel
particles include organic aerogel particles, such as
resorcinol-formaldehyde or melamine-formaldehyde aerogel particles,
and inorganic aerogel particles, such as metal oxide aerogel
particles (e.g., silica, titania, and alumina aerogels). Metal
oxide aerogel particles, especially silica aerogel particles, are
preferred. Suitable hydrophobic aerogel particles are commercially
available, and methods for preparing suitable hydrophobic aerogels
are known (see, e.g.,WO 99/36355A2; WO 99/36356A2; WO 99/36479A1;
WO 98/45210A2; WO 98/45035A1; WO 98/45032A1; WO 96/18456A2).
[0009] The hydrophobic aerogel particles desirably comprise
opacifying agents, which reduce the thermal conductivity of the
hydrophobic aerogel particles. Any suitable opacifying agent can be
used, including, but not limited to, carbon black, carbon fiber,
titania, or modified carbonaceous components as described, for
example, in WO 96/18456A2. The hydrophobic aerogel particles can
also contain fibers. Suitable fibers include any of those discussed
in the following sections.
[0010] The size of the hydrophobic aerogel particles will depend,
in part, on the desired thickness of the heat resistant aerogel
insulation composite. For the purposes of the invention the terms
"particle size" and "particle diameter" are used synonymously.
Generally, larger aerogel particles provide greater thermal
insulation; however, the aerogel particles should be relatively
small compared with the thickness of the heat resistant aerogel
insulation composite (e.g., the insulation base layer of the heat
resistant aerogel insulation composite) so as to allow the aqueous
binder to surround the hydrophobic aerogel particles and form a
matrix. For most applications, it is suitable to use hydrophobic
aerogel particles having an average particle diameter (by weight)
of about 5 mm or less (e.g., about 0.01-5 mm). Preferably,
hydrophobic aerogel particles having an average particle diameter
(by weight) of about 3 mm or less (e.g., about 0.1-3 mm) or about 2
mm or less (e.g., about 0.5-2 mm or about 1-1.5 mm). Preferably,
the hydrophobic aerogel particles used in conjunction with the
invention have a narrow particle size distribution. Thus, for
example, it is preferred to use hydrophobic aerogel particles,
wherein at least about 95% of the hydrophobic aerogel particles (by
weight) have a particle diameter of about 5 mm or less (e.g., about
0.01-5 mm), preferably about 3 mm or less (e.g., about 0.01-3 mm)
or even about 2 mm or less (e.g., about 0.5-2 mm or about 1-1.5
mm). Desirably, the hydrophobic aerogel particles are approximately
spherical in shape. The particle size and/or shape of the
hydrophobic aerogel particles can change when the particles are
combined with the other components of the high temperature aerogel
insulation composite due to the mixing process or other factors
(e.g., the hydrophobic aerogel particles can be broken). Thus, all
particle sizes and shapes mentioned above refer to the particle
sizes and shapes of the hydrophobic aerogel particles prior to
being combined with the other components of the high temperature
aerogel insulation composite. Desirably, the hydrophobic aerogel
particles have a particle size after being combined with the other
components of the high temperature aerogel insulation composite
that is about the same as the size of the hydrophobic aerogel
insulation particles prior to such combination (i.e., as described
above).
[0011] Any amount of the hydrophobic aerogel particles can be used
in the heat resistant aerogel insulation composite. For example,
the heat resistant aerogel insulation composite (e.g., the
insulation base layer of the heat resistant aerogel insulation
composite) can comprise about 5-99 vol. % hydrophobic aerogel
particles based on the total liquid/solid volume of the insulation
base layer. The total liquid/solid volume of the insulation base
layer can be determined by measuring the volume of the combined
liquid and solid components of insulation base layer (e.g.,
hydrophobic aerogel particles, binder, foaming agent, etc.). If the
insulation base layer (e.g., the binder of the insulation base
layer) is to be foamed, the total liquid/solid volume of the
insulation base layer is the volume of the combined liquid and
solid components of the insulation base layer prior to foaming. Of
course, as the proportion of hydrophobic aerogel particles
increases, the thermal conductivity of the heat resistant aerogel
insulation composite decreases, thereby yielding enhanced thermal
insulation performance; however, the mechanical strength and
integrity of the insulation base layer decreases with increasing
proportions of the hydrophobic aerogel particles due to a decrease
in the relative amount of aqueous binder used. Accordingly, it is
often desirable to use about 50-95 vol. % aerogel particles in the
insulation base layer, more preferably about 75-90 vol. % aerogel
particles.
[0012] The insulation base layer of the heat resistant aerogel
insulation composite can comprise any suitable aqueous binder. The
term aqueous binder, as used herein, refers to a binder that, prior
to being used to prepare the insulation base layer, is
water-dispersible or water-soluble. It is, therefore, to be
understood that the term aqueous binder is used to refer to an
aqueous binder in its wet or dry state (e.g., before or after the
aqueous binder has been dried or cured, in which state the binder
may no longer comprise water) even though the aqueous binder may
not be dispersible or soluble in water after the binder has been
dried or cured. The particular aqueous binder chosen should be one
that will not penetrate the surface of the hydrophobic aerogel
particles to any significant degree. Preferred aqueous binders are
those which, after drying, provide a water-resistant binder
composition. Suitable aqueous binders include, for example, acrylic
binders, silicone-containing binders, phenolic binders, vinyl
acetate binders, ethylene-vinyl acetate binders, styrene-acrylate
binders, styrene-butadiene binders, polyvinyl alcohol binders, and
polyvinyl-chloride binders, and acrylamide binders, as well as
mixtures and co-polymers thereof. The binder can be used alone or
in combination with suitable cross-linking agents. Preferred
aqueous binders are aqueous acrylic binders.
[0013] The insulation base layer of the heat resistant aerogel
insulation composite can comprise any amount of the aqueous binder.
For example, the insulation base layer can comprise 1-95 vol. % of
the aqueous binder based on the total liquid/solid volume of the
insulation base layer. Of course, as the proportion of the aqueous
binder increases, the proportion of the aerogel necessarily
decreases and, as a result, the thermal conductivity of the
insulation base layer is increased. Accordingly, it is desirable to
use as little of the aqueous binder as needed to attain a desired
amount of mechanical strength. For most applications, the
insulation base layer comprises about 1-50 vol. % aqueous binder,
or about 5-25 vol. % aqueous binder, or even about 5-10 vol. %
aqueous binder.
[0014] The insulation base layer preferably comprises a foaming
agent in addition to the aqueous binder and hydrophobic aerogel
particles. Without wishing to be bound by any particular theory,
the foaming agent is believed to enhance the adhesion between the
hydrophobic aerogel particles. Also, the foaming agent is believed
to improve the rheology of the aqueous binder (e.g., for sprayable
applications) and, especially, allows the binder to be foamed by
agitating or mixing (e.g., frothing) the combined binder and
foaming agent prior to or after the incorporation of the
hydrophobic aerogel particles, although the foaming agent can be
used without foaming the binder. In addition, a foamed binder can
be advantageously used to provide a foamed insulation base layer
having a lower density than a non-foamed base layer.
[0015] While the use of a foaming agent allows the binder to be
foamed by agitation or mixing, the binder can, of course, be foamed
using other methods, either with or without the use of a foaming
agent. For example, the binder can be foamed using compressed
gasses or propellants, or the binder can be foamed by passing the
binder through a nozzle (e.g., a nozzle that creates high-shear or
turbulent flow).
[0016] Any suitable foaming agent can be used in the insulation
base layer. Suitable foaming agents include, but are not limited
to, foam-enhancing surfactants (e.g., non-ionic, cationic, anionic,
and zwitterionic surfactants), as well as other commercially
available foam enhancing agents, or mixtures thereof. The foaming
agent should be present in an amount sufficient to enable the
aqueous binder to be foamed, if such foaming is desired.
Preferably, about 0.1-5 wt. %, such as about 0.5-2 wt. %, of the
foaming agent is used.
[0017] The insulation base layer can have any desired thickness.
Heat resistant aerogel insulation composites comprising thicker
insulation base layers have greater thermal and/or acoustic
insulation properties; however, the heat resistant aerogel
composite of the invention allows for the use of a relatively thin
insulation base layer while still providing excellent thermal
and/or acoustic insulation properties. For most applications, an
insulation base layer that is about 1- 15 mm thick, such as about
2-6 mm thick, provides adequate insulation.
[0018] The thermal conductivity of the insulation base layer will
depend, in part, upon the particular formulation used to provide
the insulation base layer. Preferably, the insulation base layer is
formulated so as to have a thermal conductivity of about 40
mW/(m.multidot.K) or less, more preferably about 35
mW/(m.multidot.K) or less, or even about 30 mW/(m.multidot.K) or
less. It is understood that the thermal conductivity of the
insulation base layer is measured after drying the insulation base
layer.
[0019] Similarly, the density of the insulation base layer will
depend, in part, upon the particular formulation used to provide
the insulation base layer. Preferably, the insulation base layer is
formulated so as to have a density of about 0.5 g/cm.sup.3 or less,
preferably about 0.3 g/cm.sup.3 or less, such as about 0.2
g/cm.sup.3 or less, or even about 0.1 g/cm.sup.3 or less (e.g.,
about 0.05 g/cm.sup.3 or less). It is understood that the density
of the insulation base layer is measured after drying the
insulation base layer.
[0020] The insulation base layer may also comprise reinforcing
fibers. The reinforcing fibers can provide additional mechanical
strength to the insulation base layer and, accordingly, to the heat
resistant insulation composite. Fibers of any suitable type can be
used, such as fiberglass, alumina, calcium phosphate mineral wool,
wollastonite, ceramic, cellulose, carbon, cotton, polyamide,
polybenzimidazole, polyaramid, acrylic, phenolic, polyester,
polyethylene, PEEK, polypropylene, and other types of polyolefins,
or mixtures thereof. Preferred fibers are heat and fire resistant,
as are fibers that do not have respirable pieces. The fibers also
can be of a type that reflects infrared radiation, such as carbon
fibers, metallized fibers, or fibers of other suitable
infrared-reflecting materials. The fibers can be in the form of
individual strands of any suitable length, which can be applied,
for example, by spraying the fibers onto the substrate with the
other components of the insulation base layer (e.g., by mixing the
fibers with one or more of the other components of the insulation
base layer before spraying, or by separately spraying the fibers
onto the substrate). Alternatively, the fibers can be in the form
of webs or netting, which can be applied, for example, to the
substrate, and the other components of the insulation base layer
can be sprayed, spread, or otherwise applied over the web or
netting. The fibers can be used in any amount sufficient to give
the desired amount of mechanical strength for the particular
application in which the heat resistant aerogel insulation
composite will be used. Typically, the fibers are present in the
insulation base layer an amount of about 0.1-50 wt. %, desirably an
amount of about 1-20 wt. %, such as an amount of about 2-10 wt. %,
based on the weight of the insulation base layer.
[0021] The thermally reflective top layer of the heat resistant
aerogel insulation composite comprises a protective binder. The
thermally reflective top layer imparts a higher degree of
mechanical strength to the heat resistant aerogel insulation
composite and/or protects the insulation base layer from
degradation due to one or more environmental factors (e.g., heat,
humidity, abrasion, impact, etc.). Thus, the thermally reflective
top layer is, preferably, substantially or completely free of
aerogel particles, which tend to reduce the strength of the
thermally reflective layer. By substantially free of aerogel
particles is meant that the thermally reflective layer contains
aerogel particles in an amount of about 20 vol. % or less, such as
about 10 vol. % or less, or even about 5 vol. % or less (e.g.,
about 1 vol. % or less). The protective binder can be any suitable
binder that is resistant to the particular conditions (e.g., heat,
stress, humidity, etc.) to which the heat resistant aerogel
insulation composite will be exposed. Thus, the selection of the
binder will depend, in part, upon the particular properties desired
in the heat resistant aerogel insulation composite. The protective
binder can be the same or different from the aqueous binder of the
insulation base layer. Suitable binders include aqueous and
non-aqueous natural and synthetic binders. Examples of such binders
include any of the aqueous binders suitable for use in the
insulation base layer, as previously described herein, as well as
non-aqueous binders. Preferred binders are aqueous binders, such as
aqueous acrylic binders. Especially preferred are self-crosslinking
binders, such as self-crosslinking acrylic binders.
[0022] The infrared reflecting agent can be any compound or
composition that reflects or otherwise blocks infrared radiation,
including opacifiers such as carbon black, carbon fibers, titania
(rutile), and metallic and non-metallic particles, fibers,
pigments, and mixtures thereof. Preferred infrared reflecting
agents include metallic particles, pigments, and pastes, such as
aluminum, stainless steel, copper/zinc alloys, and copper/chromium
alloys. Aluminum particles, pigments, and pastes are especially
preferred. In order to prevent the infrared reflecting agent from
settling in the protective binder, the thermally reflective top
layer advantageously comprises an anti-sedimentation agent.
Suitable anti-sedimentation agents include commercially available
fumed metal oxides, clays, and organic suspending agents. Preferred
anti-sedimentation agents are fumed metal oxides, such as fumed
silica, and clays, such as hectorites. The thermally reflective
layer also can comprise a wetting agent, such as a non-foaming
surfactant.
[0023] Preferred formulations of the thermally reflective top layer
comprise reinforcing fibers. The reinforcing fibers can provide
additional mechanical strength to the thermally reflective top
layer and, accordingly, to the heat resistant insulation composite.
Fibers of any suitable type can be used, such as fiberglass,
alumina, calcium phosphate mineral wool, wollastonite, ceramic,
cellulose, carbon, cotton, polyamide, polybenzimidazole,
polyaramid, acrylic, phenolic, polyester, polyethylene, PEEK,
polypropylene, and other types of polyolefins, or mixtures thereof.
Preferred fibers are heat and fire resistant, as are fibers that do
not have respirable pieces. The fibers also can be of a type that
reflects infrared radiation, and can be used in addition to, or
instead of, the infrared reflecting agents previously mentioned.
For example, carbon fibers or metallized fibers can be used, which
provide both reinforcement and infrared reflectivity. The fibers
can be in the form of individual strands of any suitable length,
which can be applied, for example, by spraying the fibers onto the
substrate with the other components of the thermally reflective
layer (e.g., by mixing the fibers with one or more of the other
components of the thermally reflective layer before spraying, or by
separately spraying the fibers onto the insulation base layer).
Alternatively, the fibers can be in the form of webs or netting,
which can be applied, for example, to the insulation base layer,
and the other components of the thermally reflective layer can be
sprayed, spread, or otherwise applied over the web or netting. The
fibers can be used in any amount sufficient to give the desired
amount of mechanical strength for the particular application in
which the heat resistant aerogel insulation composite will be used.
Typically, the fibers are present in the thermally reflective top
layer in an amount of about 0.1-50 wt. %, desirably an amount of
about 1-20 wt. %, such as an amount of about 2-10 wt. %, based on
the weight of the thermally reflective layer.
[0024] The thickness of the thermally reflective top layer will
depend, in part, on the degree of protection and strength desired.
While the thermally reflective top layer can be any thickness, it
is often desirable to keep the thickness of the heat resistant
aerogel insulation composite to a minimum and, thus, to reduce the
thickness of the thermally reflective top layer to the minimum
amount needed to provide an adequate amount of protection for a
particular application. Generally, adequate protection can be
provided by a thermally reflective top layer that is about 1 mm
thick or less.
[0025] The thermal conductivity of the heat resistant aerogel
insulation composite will depend, primarily, on the particular
formulation of the insulation base layer, although the formulation
of the thermally reflective coating may have some effect.
Preferably, the heat resistant aerogel insulation composite is
formulated so as to have a thermal conductivity of about 40
mW/(m.multidot.K) or less, more preferably about 35
mW/(m.multidot.K) or less, or even about 30 mW/(m.multidot.K) or
less.
[0026] The term "heat resistant" as it is used to describe the
aerogel insulation composite of the invention means that the
aerogel insulation composite will not substantially degrade under
high heat conditions. An aerogel insulation composite is considered
to be heat resistant within the meaning of the invention if, after
exposure to high-heat conditions as described in Example 1 for a
period of 1 hour, the aerogel insulation composite retains at least
about 85%, preferably at least about 90%, more preferably at least
about 95%, or even at least about 98% or all of its original mass.
Specifically, the high heat conditions are provided using a 250 W
heating element (IRB manufactured by Edmund Buhler GmbH, Germany)
connected to a hot-air blower (HG3002 LCD manufactured by Steinel
GmbH, Germany) with thin aluminum panels arranged around the device
to form a tunnel. The aerogel insulation composite is exposed to
the high heat conditions (thermally reflective layer facing the
heating element) at a distance of about 20 mm from the heating
element, wherein the hot air blower (at full blower setting and
lowest heat setting) provides a continuous flow of air between the
heating element and the aerogel insulation composite. Desirably,
the heat resistant aerogel insulation composite does not visibly
degrade under such conditions.
[0027] When the heat resistant aerogel insulation composite is to
be used under conditions of a certain flammability classification,
for example, where it could be exposed to open-flames or extremely
high-temperature conditions, the aerogel insulation desirably
includes a suitable fire retardant. The fire retardant can be
included in the insulation base layer and/or the thermally
reflective top layer of the heat resistant aerogel insulation
composite. Suitable fire retardants include aluminum hydroxides,
magnesium hydroxides, ammonium polyphosphates and various
phosphorus-containing substances, and other commercially available
fire retardants and intumescent agents.
[0028] The heat resistant aerogel insulation composite (e.g., the
insulation base layer and/or the thermally reflective layer of the
aerogel insulation composite) may additionally comprise other
components, such as any of various additives known in the art.
Examples of such additives include rheology control agents and
thickeners, such as fumed silica, polyacrylates, polycarboxylic
acids, cellulose polymers, as well as natural gums, starches and
dextrins. Other additives include solvents and co-solvents, waxes,
surfactants, and curing and cross-linking agents, as required,
provided they are used in amounts such that they do not cause the
binder system to penetrate the hydrophobic aerogel particles to any
significant degree.
[0029] Method for Preparing a Heat Resistant Aerogel Insulation
Composite and Aerogel Binder Composition
[0030] The invention further provides a method for preparing a heat
resistant aerogel insulation composite comprising, consisting
essentially of, or consisting of (a) providing on a substrate an
insulation base layer comprising, consisting essentially of, or
consisting of hydrophobic aerogel particles, an aqueous binder,
and, optionally, a foaming agent, and (b) applying to a surface of
the insulation base layer a thermally reflective top layer
comprising a protective binder and an infrared reflecting agent.
The various elements of the heat resistant aerogel insulation
composite prepared in accordance with this method are as previously
described herein.
[0031] The insulation base layer can be provided by any suitable
method. For example, the hydrophobic aerogel particles and aqueous
binder can be combined by any suitable method to form an aerogel
binder composition, which then can be applied to the substrate to
form an insulation base layer, for example, by spreading or
spraying the aerogel binder composition on the substrate.
[0032] Preferably, however, the insulation base layer is provided
by another method of the invention. In particular, the insulation
base layer is provided by (a) providing a binder composition
comprising, consisting essentially of, or consisting of an aqueous
binder and a foaming agent, (b) agitating the binder composition to
provide a foamed binder composition, (c) combining the foamed
binder composition with the hydrophobic aerogel particles to
provide an aerogel binder composition, and (d) applying the aerogel
binder composition to the substrate to provide the insulation base
layer. Alternatively, the insulation base layer can be provided by
(a) providing a binder composition comprising, consisting
essentially of, or consisting of an aqueous binder and, optionally,
a foaming agent to provide a binder composition, (b) providing an
aerogel composition comprising, consisting essentially of, or
consisting of hydrophobic aerogel particles, and (c) simultaneously
applying the binder composition and the aerogel composition to the
substrate, wherein the binder composition is mixed with the aerogel
composition to provide the insulation base layer. The aerogel
composition comprises, consists essentially of, or consists of
hydrophobic aerogel particles, as previously described herein, and,
optionally, a suitable vehicle. The binder composition and/or
aerogel composition can be applied to the substrate in accordance
with the invention (e.g., together or separately) by any suitable
method, such as by spreading or, preferably, spraying the aerogel
binder composition or the components thereof onto the substrate. By
"simultaneously applying" is meant that the aerogel composition and
the binder composition are separately delivered to the substrate at
the same time, wherein the aerogel composition and the binder
composition are mixed during the delivery process (e.g., mixed in
the flow path or on the substrate surface). This can be
accomplished, for example, by simultaneously spraying the aerogel
composition and the binder composition on the substrate, whereby
the aerogel composition and binder composition are delivered via
separate flowpaths. The flowpaths can be joined within the spraying
apparatus, such that a combined aerogel-binder composition is
delivered to the substrate, or the flowpaths can be entirely
separate, such that the aerogel composition is not combined with
the binder composition until the respective compositions reach the
substrate.
[0033] In this regard, the invention provides a method for
preparing an aerogel binder composition, as well as a composition
prepared by such a method, which can be used to provide the
insulation base layer of the heat resistant aerogel insulation
composite, or can be used for other purposes. In particular, the
method for preparing an aerogel binder composition comprises,
consists essentially of, or consists of (a) providing a binder
composition comprising, consisting essentially of, or consisting of
an aqueous binder and a foaming agent, (b) agitating the binder
composition to provide a foamed binder composition, and (c)
combining the foamed binder composition with hydrophobic aerogel
particles to provide an aerogel binder composition. Alternatively,
the aerogel binder composition can be prepared in accordance with
the present invention by a method comprising (a) providing a binder
composition comprising, consisting of, or consisting essentially of
an aqueous binder and, optionally, a foaming agent, (b) providing
an aerogel composition comprising, consisting essentially of, or
consisting of hydrophobic aerogel particles, and (c) simultaneously
applying the binder composition and the aerogel composition to a
substrate, whereupon the binder composition is mixed with the
aerogel composition to provide an aerogel binder composition.
[0034] By combining the hydrophobic aerogel particles with the
binder composition according to these process steps, an aerogel
binder composition having desirable, if not unique, properties can
be provided, which aerogel composition is yet another aspect of the
invention. In particular, and without wishing to be bound to any
particular theory, the aerogel binder compositions produced in
accordance with the invention exhibit a reduced tendency to
"wet-out" the aerogel particles, thereby increasing the thermal
conductivity of the aerogel binder composition. Also, the method of
the invention enables the use of a high aerogel to binder ratio,
which enhances the thermal performance of the aerogel binder
composition and reduces the density of the aerogel binder
composition. Furthermore, the method of the invention provides a
sprayable aerogel binder composition, allowing flexibility in the
application and use of the aerogel binder composition. The
hydrophobic aerogel particles, binder composition, and foaming
agent are as previously described herein with respect to the
aerogel insulation composition.
[0035] While the binder, alone or in combination with the foaming
agent, is, preferably, foamed by agitation or mixing, other foaming
methods can be used. For example, the binder can be foamed using
compressed gasses or propellants, or the binder can be foamed by
passing the binder through a nozzle (e.g., a nozzle that creates
high-shear or turbulent flow).
[0036] The thermally reflective top layer of the heat resistant
aerogel insulation composite can be applied to the surface of the
insulation base layer by any suitable method. The components of the
thermally reflective top layer are as previously described herein.
Preferably, the components of the thermally reflective top layer
are combined, with mixing, to provide a thermally reflective
coating composition, which then is applied to the surface of the
insulation base layer by any suitable method, for example, by
spreading or spraying.
[0037] While adhesives or coupling agents may be used to adhere the
thermally reflective top layer to the insulation base layer, such
adhesives are not needed in accordance with the invention inasmuch
as the binder in the insulation base layer or thermally reflective
top layer can provide desired adhesion. The thermally reflective
top layer is, preferably, applied to the insulation base layer
while the insulation base layer is wet, but can be applied after
the insulation base layer has been dried. The aerogel insulation
composite (e.g., the insulation base layer and/or the thermally
reflective top layer of the aerogel insulation composite) or
aerogel binder composition can be dried under ambient conditions or
with heating, for example, in an oven.
[0038] Applications and End-Uses
[0039] The heat resistant aerogel insulation composite and aerogel
binder composition of the invention, as well as the methods for
their preparation, can, of course, be used for any suitable
purpose. However, the heat resistant aerogel insulation composite
and aerogel binder composition of the invention are especially
suited for applications demanding insulation that provides thermal
stability, mechanical strength, and/or flexibility in the mode of
application. For instance, the heat-resistant aerogel insulation
composite, according to preferred formulations, especially
sprayable formulations, is useful for insulating surfaces from high
temperatures and can be easily applied to surfaces which might
otherwise be difficult or costly to protect by conventional
methods. Examples of such applications include various components
of motorized vehicles and devices, such as the engine compartment,
firewall, fuel tank, steering column, oil pan, trunk, and spare
tire, or any other component of a motorized vehicle or device. The
heat resistant aerogel insulation composite is especially well
suited for insulating the underbody of a motorized vehicle,
especially as a shield for components near the exhaust system. Of
course, the heat resistant aerogel insulation composite and aerogel
binder composition of the invention can be used to provide
insulation in many other applications. For instance, the heat
resistant aerogel insulation composite and aerogel binder
composition can be used to insulate pipes, walls, and heating or
cooling ducts. While preferred formulations of the heat resistant
aerogel insulation composite and aerogel binder composition are
sprayable formulations, the heat resistant aerogel insulation
composite and aerogel binder composition can also be extruded or
molded to provided insulation articles such as tiles, panels, or
various shaped articles. In this regard, the invention also
provides a substrate, such as any of those previously mentioned,
comprising the heat resistant aerogel insulation composite or
aerogel binder composition of the invention, as well as a method
for insulating a substrate comprising the use of any of the heat
resistant aerogel insulation composite, aerogel binder composition,
or methods for their preparation or use.
[0040] The following examples further illustrate the invention but,
of course, should not be construed as in any way limiting its
scope.
EXAMPLE 1
[0041] This example illustrates the preparation and performance of
a heat resistant aerogel insulation composite in accordance with
the invention.
[0042] An aerogel binder composition was prepared by combining 200
g of an aqueous acrylic binder (LEFASOL.TM. 168/1 manufactured by
Lefatex Chemie GmbH, Germany), 1.7 g of a foaming agent
(HOSTAPUR.TM. OSB manufactured by Clariant GmbH, Germany), and 30 g
of an ammonium polyphosphate fire retardant (EXOLIT.TM. AP420
manufactured by Clariant GmbH, Germany) in a conventional mixer.
The aerogel binder composition was mixed until 3 dm.sup.3 of a
foamed binder composition was obtained. Subsequently, 100 g of
opacified, hydrophobic aerogel beads (NANOGEL.TM. beads
manufactured by Cabot Nanogel GmbH, Germany) were slowly added with
mixing to maintain the volume at 3 dm.sup.3, thereby providing an
aerogel-binder composition.
[0043] A thermally reflective coating composition was prepared by
combining 58 g of an aqueous acrylic binder (WORLEECRYL.TM. 1218
manufactured by Worlee Chemie GmbH, Germany) with 22.6 g of a fumed
silica anti-sedimentation agent (CAB-O-SPERSE.TM. manufactured by
Cabot Corporation, Massachusetts) and 19.4 g of an aluminum pigment
paste as an infrared reflecting agent (STAPA.TM. Hydroxal WH 24
n.l. manufactured by Eckart GmbH, Germany). The composition was
gently mixed using a magnetic stirrer.
[0044] Four square (10 cm.times.10 cm) test panels of thermoplastic
molding were cut from the molded part of the underbody of an
automobile. The first test panel (panel 1A) was left uncovered. The
second test panel (panel 1B) was shielded with a conventional
aluminum heat-shield of the type used to protect the automobile
underbody from the heat of an exhaust system. The third test panel
(panel 1C) was coated with the aerogel binder composition. The
fourth test panel (panel 1D) was coated with the aerogel binder
composition to provide a base insulation layer as well as the
thermally reflective composition to provide a thermally reflective
top layer, thereby providing a heat resistant aerogel insulation
composite. The aerogel binder composition and thermally reflective
composition were applied to the test panels by conventional spray
techniques. The panels were dried for two hours at 130.degree. C.
in a paint-drying oven.
[0045] Thereafter, each of the four pieces of thermoplastic molding
was exposed to a 250 W heating element (IRB manufactured by Edmund
Buhler GmbH, Germany) connected to a hot-air blower (HG3002 LCD
manufactured by Steinel GmbH, Germany). The heating element was
mounted vertically, and the test panel held vertically
approximately 20 mm from the hot surface; corks were used as
spacers. The outlet of the hot-air blower was set so that it was
about 12 cm from the heater element, and arranged to provide a
continual flow of air between the heater surface and the test panel
(full setting). Three thin, rectangular aluminum panels
(40.times.20 cm) were arranged around the device to form a tunnel.
A temperature probe was placed in contact with the rear of the test
panel using heat-sink grease to ensure good thermal contact. The
temperature of the test panel was displayed on a digital
thermometer. The test panel was exposed to the heating element
until the temperature stabilized, or until severe thermal damage
could be seen. The results are given in Table 1, below.
1TABLE 1 Temp. Heating Panel Sample (.degree. C.) Time Observations
1A Plastic 142* 10 min Decomposition of the plastic occurred 1B
Plastic and a conventional 39 1 h No decomposition aluminum heat
shield visible 1C Plastic coated with an 66 30 min Decomposition of
aerogel binder the aerogel- composition containing layer occurred
1D Plastic coated with an 46 2.5 h No decomposition aerogel
insulation visible composite *This experiment was terminated before
a stable temperature was reached since the plastic piece was
beginning to decompose quite markedly.
[0046] The results show that, without a shield or coating, the
thermoplastic sample (panel 1A) was quickly damaged by the heat.
Also, the single aerogel-containing layer (without the thermally
reflective top-coat) (panel 1C) decomposed under the high heat
conditions, although the temperature reached on the rear of the
panel was only about 66.degree. C. Both the conventional aluminum
heat-shield (sample 1B) and the aerogel composite system of the
invention (sample 1D) prevented thermal damage to the thermoplastic
sample and kept the temperature relatively low.
EXAMPLE 2
[0047] The following example illustrates the preparation and
thermal conductivity of a heat resistant aerogel insulation
composite in accordance with the invention.
[0048] An aerogel binder composition was prepared as follows: 200 g
of an aqueous acrylic binder (LEFASOL.TM. manufactured by Lefatex
Chemie GmbH, Germany), 30 g of ammonium phosphate flame retardant
(EXOLIT.TM. AP420 manufactured by Clariant GmbH, Germany), and 1.7
g of a foaming agent (HOSTAPUR.TM. OSB manufactured by Clariant
GmbH, Germany) were combined and mixed in a conventional mixer at
medium speed until thoroughly foamed. 100 g of opacified aerogel
particles (NANOGEL.TM. beads manufactured by Cabot Nanogel GmbH,
Germany) were slowly added to the foamed binder composition to
provide an aerogel binder composition.
[0049] Two thermally reflective coating compositions (coating
compositions 2A and 2B) were prepared by combining 13.0 g of an
aluminum pigment (CHROMAL X.TM. manufactured by Eckart GmbH,
Germany), 27.3 g de-ionized water, and 55.6 g of an acrylic binder
(Composition 2A--WORLEECRYL.TM. 1218 manufactured by Worlee Chemie
GmbH, Germany; Composition 2B--LEFASOL.TM. manufactured by Lefatex
Chemie GmbH, Germany).
[0050] A 20.times.20 cm form was covered by aluminum foil for
sample preparation. A first sample (sample 2A) was prepared by
spraying the aerogel binder composition onto the form using a
spraygun at 4-bar pressure. Immediately afterwards, coating
composition 2A was sprayed onto the surface of the aerogel binder
composition using a spraygun at 2-bar pressure. A second sample
(sample 2B) was prepared by the same procedure, except that coating
composition 2B was used. The samples had a thickness of
approximately 12 mm. The samples were dried for more than 90
minutes at 130 C, and the thermal conductivity of each sample was
measured using a LAMDA CONTROL.TM. A50 thermal conductivity
instrument (manufactured by Hesto Elektronik GmbH, Germany). After
an initial thermal conductivity measurement was taken, a second
coat of coating composition 2A was applied to sample 2A, and a
second thermal conductivity measurement was taken. The results are
presented in Table 2.
2 TABLE 2 Thermal Conductivity Sample [mW/(m .multidot. K)] 2A 32.0
2A (twice coated) 32.3 2B 31.5
[0051] These results demonstrate that aerogel composites, which
have low thermal conductivity, can be prepared in accordance with
the invention.
[0052] All references, including publications, patent applications,
and patents, cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
[0053] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) are to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context. The terms "comprising,"
"having," "including," and "containing" are to be construed as
open-ended terms (i.e., meaning "including, but not limited to,")
unless otherwise noted. Recitation of ranges of values herein are
merely intended to serve as a shorthand method of referring
individually to each separate value falling within the range,
unless otherwise indicated herein, and each separate value is
incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0054] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. Variations of those preferred embodiments may
become apparent to those of ordinary skill in the art upon reading
the foregoing description. The inventors expect skilled artisans to
employ such variations as appropriate, and the inventors intend for
the invention to be practiced otherwise than as specifically
described herein. Accordingly, this invention includes all
modifications and equivalents of the subject matter recited in the
claims appended hereto as permitted by applicable law. Moreover,
any combination of the above-described elements in all possible
variations thereof is encompassed by the invention unless otherwise
indicated herein or otherwise clearly contradicted by context.
* * * * *